1. Field of the Invention
The present invention relates to a transmission rate control method, a transmission rate control system, and a mobile station.
2. Description of the Related Art
In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message of a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 1, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has been also a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data is generated as shown in FIG. 2A, the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 2B, or, as shown in FIG. 2C, by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIGS. 2B and 2C.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
As described in the Non-patent literature (3GPP TSG-RAN TS25.309 v6.2.0), in the Enhanced Uplink (EUL), it is required to transmit a scheduling request (RR: Rate Request) to a radio base station, so as to receive a scheduling grant signal (scheduling Grant) from the radio base station, for a channel (EDCH) to which a transmission rate control is applied. Here, the radio base station transmits the Scheduling Grant in response to the RR transmitted by EDCH.
In addition, performing a transmission based on a transmission rate which is defined per a logical channel, without using the. Scheduling Grant, can be implemented in Non-scheduled Transmission. However, the logical channel, which is defined as Non-scheduled Transmission, can not control the transmission rate using the Scheduling Grant.
Accordingly, as shown in FIG. 12, in the channel to which the transmission rate control is applied, a transmission of data can be started after transmitting RR to the radio base station and receiving the Absolute Grant channel (AGCH) as the Scheduling Grant from the radio base station.
Referring to FIG. 3, the operation before starting transmission of uplink user data in the Enhanced Uplink (EUL) will be described.
As shown in FIG. 3, at step (1), a mobile station UE transmits a call setup request to a radio network controller RNC, in other words, the mobile station UE calls.
At steps (2) to (6), the radio network controller RNC performs a call setup processing with cooperating with the mobile station UE and a radio base station Node B, in response to the call setup request.
At step (7), the mobile station UE transmits the above mentioned scheduling request (RR) when data to be transmitted is generated, receives an Absolute Grant Channel as the Scheduling Grant from the radio base station Node B, and starts transmission of uplink user data via a user data channel (E-DPDCH) at a transmission determined based on the received Absolute Grant Channel.
FIGS. 4 to 6 show a configuration of a radio communication function of mobile station which is used for the Enhanced Uplink (EUL), FIGS. 7 to 9 show a configuration of a radio base station which is used for the Enhanced Uplink (EUL), and FIG. 10 shows a configuration of a radio network controller which is used for the Enhanced Uplink (EUL).
In the radio communication function of mobile station, an E-TFC selecting section as shown in FIG. 6 is configured to control a transmission rate of uplink user data to be transmitted via an E-DPDCH, based on an Absolute Grant Channel (AGCH) as a Scheduling Grant transmitted from the radio base station.
Here, as shown in FIG. 13, the mobile station UE is configured to receive the Absolute Grant Channel (AGCH) from a cell #21 which functions as a serving cell of the mobile station UE, when performing a soft handover processing between a cell #13 in a radio base station Node B #1 and the cell #21 in a radio base station Node B #2.
Generally, if not otherwise specified, a radio base station means a cell in the radio base station, in the field of the Enhanced Uplink (EUL).
In the radio base station, a scheduling section as shown in FIG. 9 is configured to determine and transmit an Absolute Grant Channel (AGCH) which is common in a cell or an Absolute Grant Channel (AGCH) which is dedicated to each serving mobile station.
Here, a serving mobile station for a specified cell is a mobile station which serving cell is the cell.
Generally, if not otherwise specified, a transmission rate includes a transport block size and a transmission power ratio (a ratio of an E-DPDCH transmission power to a DPCCH transmission power), in the field of the Enhanced Uplink (EUL).
However, as described above, there has been a problem that when a data which is to be transmitted is generated, a mobile station can not transmit data until receiving the Scheduling Grant, in the communication using the EUL.
Further, even if the transmission of data is implemented without using the Scheduling Grant, this has been a problem that the transmission rate control can not performed in the Non-scheduled Transmission.
Furthermore, a delay for the transmission rate control occurs, which leads to a deterioration of a channel quality.